amber workshop grenoble march 2007 jörg-uwe pott i. physik. institut university of cologne, germany...
TRANSCRIPT
AMBER workshop Grenoble March 2007
Jörg-Uwe Pott
I. Physik. Institut
University of Cologne, Germany
VLTI observations of the central parsec of our Galaxy
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• Introduction to the Galactic Center (GC; central pc)
• Observational results achieved with AMBER
• Outlook for AMBER & PRIMA
Outline of the presentation:
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
The center of the Milky Way is the nearest nucleus of a galaxy:– harbors closest supermassive BHs (SMBH, 3*106M⊙) at
only 8 kpc distance (1as~40mpc)– next similar galactic nucleus (Andromeda) is 100x farther– unique to study SMBH-host interaction– we have to understand star formation in the immediate
vicinity of a SMBH and investigate the typical radiative properties to understand spatially unresolved observations
) Intro ) Observations ) Outlook
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• Current knowledge of the central stellar cluster:– lots of hot and massive stars ionizing the local ISM– indications for favoured massive star formation,
‘top-heavy IMF‘
– solar metallicity, ongoing star formation, Avis25
) Intro ) Observations ) Outlook
< GCIRS 7, K=6.5
< Sgr A*
J&K two color K-Naco
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• Current knowledge of the central stellar cluster (II):– stellar cusp due to the gravitational potential of the SMBH
appears in stellar number counts– single telescope confusion limit at K~16mag (seeing
limited) and K~17-18mag (AO-limited at 8, class teles.)
) Intro ) Observations ) Outlook
Sch
ödel
+‘0
7
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• Current knowledge of the central stellar cluster (III):– indications for a central outflow of SgrA*, of unknown
importance for the stellar surroundings– a lot of warm dust in the MIR, shock-heated material,
ionized gas – VLTI/MIDI can be used to study dust formation:
) Intro ) Observations ) Outlook
Pot
t+’0
6,‘0
7
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• Why to search for binaries at the GC with VLTI?– help to understand / distinguish stellar properties of the
central cluster and local star formation– dust formation in windy binary systems– analyze recently found ‘comoving groups‘ like IRS13E
and IRS16 cluster, which have been suggested to harbour intermediate mass black holes of 103-4M⊙
• AMBER advantages:– the closure phase can be more sensitive to binaries than
the visibility measurements (e.g. Weigelt+’07)– only UT interferometry is sensitive enough for GC– only OLBI has sufficient angular resolution (currently only
one eclipsing binary is known: IRS 16SW, Ott+‘99)
) Intro ) Observations ) Outlook
Sch
ödel
+‘0
5
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• Current phase of the project:– facing the real life: start to observe and gain
experience (e.g.: learn how to select frames...)– AMBER with UTs in LR-mode is the only option due
to sensitivity
– first target: GCIRS7: red M1 supergiant, Teff=3600K, expected diameter: 0.5mas, if there is NO hot dust!
NIR dust emission
MIR
-10
m M
IDI
obs
) Intro ) Observations ) Outlook
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• First observational results:visibility could be
measured and
calibrated at
short baseline (U3-U4),
but still low SNR
Raw visibilities: where is my banana?
GCIRS 7 HD 153368
best 30%
best 30%
best 10%
best 10%
• Think positive: Data might indicate:– calibrated visibility slightly increase with wavelength– 0.9Vis0.95 -> target slightly resolved -> 2mas– extended structure / binary possible
) Intro ) Observations ) Outlook
Special thanks to S. Kraus, MPIfR
0.8--
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• Feasibility of GC-AMBER observations was demonstrated– aggravating circumstances (high airmass, baseline
tracking problems, strong piston error due to LR-mode, bright calibrator etc.) avoided the measurement of CP, longer baseline visibilities and higher accuracy in Mar06
• Phase referencing on GCIRS7 appears to be possible
• Extended structure might exist– > telescope time was awarded to redo this pioneering
study and measure the long baseline visibilities and the closure phase in LR-mode in May07
) Intro ) Observations ) Outlook
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
• Potential sources for (phase-referenced) AMBER observations:– current Klim~9-10mag (Petrov+‘07), UT-vibro limited
– already potential Klim~11 would help
– off-axis phase-referencing with PRIMA/STS and FSU or FINITO will dramatically increase No. of targets
– even SgrA* NIR-flares (Genzel, Eckart+) are within reach
Sources around the Galactic Center Black Hole
0
0.5
1
1.5
2
2.5
3
3.5
8 10 12 14 16 18
K-band Magnitude
Rad
ius
(arc
sec)
R(1995.4)
Rmin
[dat
a: G
hez+
’98,
‘05]
) Intro ) Observations ) Outlook
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
[Sch
ödel
+’0
4]
• Future: PRIMA astrometry at the GC to increase precision of stellar orbit measurements and prove the existence non-Keplerian due to GeneralRelativity
– several orbiting S-Stars (K=14..15: #5; K=15..17: #12) within 0.5 arcsec to SgrA*
– stellar multiplicity and background influence of theses stars have to be known to understand astrometric errors (impact on spatial filtering)
– >AMBER measurements can help to investigate these errors
) Intro ) Observations ) Outlook
Jörg-Uwe Pott, ‘VLTI observations of the central parsec of our Galaxy’; contact: [email protected]
Thank You for your attention!
Any questions?